This present invention relates to methods and apparatus for applying hydrogels within body lumens to occlude, coat or support tissue. More particularly, the present invention relates apparatus and methods for intraluminally delivering two or more liquid components to form a hydrogel implant in situ.
Hydrogels are materials that absorb solvents (such as water), undergo rapid swelling without discernible dissolution, and maintain three-dimensional networks capable of reversible deformation. See, e.g., Park, et al., Biodegradable Hydrogels for Drug Delivery, Technomic Pub. Co., Lancaster, Pa. (1993).
Hydrogels may be uncrosslinked or crosslinked. Uncrosslinked hydrogels are able to absorb water but do not dissolve due to the presence of hydrophobic and hydrophilic regions. A number of investigators have explored the concept of combining hydrophilic and hydrophobic polymeric components in block (Okano, et al., xe2x80x9cEffect of hydrophilic and hydrophobic microdomains on mode of interaction between block polymer and blood plateletsxe2x80x9d, J. Biomed. Mat. Research, 15:393-402 (1981), or graft copolymeric structures (Onishi, et al., in Contemporary Topics in Polymer Science, (Bailey and Tsuruta, Eds.), Plenum Pub. Co., New York, 1984, p. 149), and blends (Shah, xe2x80x9cNovel two-phase polymer system,xe2x80x9d Polymer, 28:1212-1216 (1987) and U.S. Pat. No. 4,369,229 to Shah) to form the xe2x80x9chydrophobic-hydrophilicxe2x80x9d domain systems, which are suited for thermoplastic processing. See, Shah, Chap. 30, in Water Soluble Polymers (Shalaby et al., Eds.), Vol. 467, ACS-Symp. Ser., Amer. Chem. Soc., Washington (1991). These uncrosslinked materials can form hydrogels when placed in an aqueous environment.
Covalently crosslinked networks of hydrophilic polymers, including water-soluble polymers are traditionally denoted as hydrogels (or aquagels) in the hydrated state. Hydrogels have been prepared based on crosslinked polymeric chains of methoxypoly(ethylene glycol) monomethacrylate having variable lengths of the polyoxyethylene side chains, and their interaction with blood components has been studied (Nagaoka et al., in Polymers as Biomaterial (Shalaby et al., Eds.) Plenum Press, 1983, p. 381). A number of aqueous hydrogels have been used in various biomedical applications, such as, for example, soft contact lenses, wound management, and drug delivery.
Non-degradable hydrogels made from poly(vinyl pyrrolidone) and methacrylate have been fashioned into fallopian tubal occluding devices that swell and occlude the lumen of the tube. See, Brundin, xe2x80x9cHydrogel tubal blocking device: P-Blockxe2x80x9d, in Female Transcervical Sterilization, (Zatuchini et al., Eds.) Harper Row, Philadelphia (1982). Because such hydrogels undergo a relatively small amount of swelling and are not absorbable, so that the sterilization is not reversible, the devices described in the foregoing reference have found limited utility.
It therefore would be desirable to provide methods and apparatus of using hydrogel materials to temporarily occlude a body lumen that overcome the drawbacks of previously known compositions and methods.
Abnormal vascular connections, known as arteriovenous malformations (AVMs), may develop either as a congenital defect or as a result of iatrogenic or other trauma. An AVM may lead to a substantial diversion of blood from the intended tissue and may consequently engender a variety of symptoms, including those leading to morbidity. Subdural hematomas and bleeding also may occur as a result of the presence of an AVM.
Surgical intervention is often undertaken to correct AVMs. Interventional radiologic approaches also are used to obliterate AVMs by embolization, in which the goal of embolization is to selectively obliterate an abnormal vascular structure, while preserving blood supply to surrounding normal tissue. Embolization typically is accomplished using low-profile soft microcatheters that allow superselective catheterization into the brain to deliver an embolic material under fluoroscopic guidance. Various embolic materials have been used in endovascular treatment in the central nervous system, such as cyanoacrylates, ethylene-vinyl alcohol copolymer mixtures, ethanol, estrogen, poly(vinyl acetate), cellulose acetate polymer, poly (vinyl alcohol), gelatin sponges, microfibrillar collagen, surgical silk sutures, detachable balloons, and coils. Delivery of these embolic materials often requires the use of elaborate delivery systems.
It would therefore be desirable to provide methods and apparatus for using multi-component hydrogel systems as embolic materials to occlude arteriovenous malformations, thus taking advantage of the relative ease with which the crosslinkable components of a hydrogel system may be delivered.
U.S. Pat. No. 5,785,679 to Abolfathi et al. describes methods and apparatus for excluding aneurysms with in-situ moldable agents, such as water-swellable and thermally initiated hydrogels, by intraluminally or laparoscopically injecting the moldable material around an inflatable member disposed in the vessel. The reference also describes embedding a stent in the moldable material for enhanced support. International Publication No. WO 95/08289 describes a similar system for excluding aneurysms using photopolymerizable materials. Both systems employ inflatable members that partially or completely occlude the vessel and mold the moldable material during polymerization.
It would therefore be desirable to provide methods and apparatus for excluding aneurysms using hydrogels that are formed in situ, without partially or completely occluding the vessel.
In view of the foregoing, it is an object of the present invention to provide methods and apparatus of using hydrogel materials to temporarily occlude a body lumen that overcome the drawbacks of previously known compositions and methods.
It is another object of this invention to provide methods and apparatus for using multi-component hydrogel systems as embolic materials to occlude arteriovenous malformations, thus taking advantage of the relative ease with which the crosslinkable components of a hydrogel system may be delivered.
It is a further object of the present invention to provide methods and apparatus for excluding aneurysms using hydrogels that are formed in situ, without partially or completely occluding the vessel.
These and other objects of the invention are accomplished by providing apparatus and methods for delivering and applying crosslinkable compositions (referred to herein as xe2x80x9cprepolymersxe2x80x9d) to selected tissue lumens, and then initiating a reaction in situ by allowing the prepolymers to either mix with other prepolymers and initiate a crosslinking process, or to be exposed to the physiological environment to initiate the crosslinking process. The crosslinkable solutions used with the apparatus may be crosslinked using either physical crosslinking, chemical crosslinking, or both.
In accordance with the present invention, delivery systems are provided for delivering separate prepolymer components of a hydrogel system, without premature crosslinking within the delivery system. In one embodiment, the delivery system includes an occlusive element for anchoring a distal end and isolating the region in which the hydrogel is to be formed in situ. In another embodiment, the delivery system may include variable stiffness regions to enable passage through tortuous anatomy. In yet another embodiment, the delivery system includes a steerable tip. In still further alternative embodiments, the prepolymer components of the hydrogel system may be mixed together in a mixing chamber disposed in a distal region of the delivery system, and then extruded into the body lumen or void during the crosslinking process, to reduce washout or dilution of the components.
Methods of using the inventive apparatus to apply a polymeric material to a lumen as a coating, or to fill in a luminal defect, such as an aneurysm, to occlude an abnormal vascular structure, such as an arteriovenous malformation or arteriovenous fistula whether natural or induced, and to occlude a natural lumen for a therapeutic purpose, within a human or animal patient, also are provided.